When Two Become One
by docere
Summary: Twenty years ago Genkai adopted a girl from an unknown world. Now a portal to that world has finally been discovered and some demons have found their way across. May, Kurama, and Hiei must adapt themselves to this strange new world, figure out the demons' plans, and stop them before it's too late. Crossover YYH and HxH but no HxH knowledge required. Slight KuramaxOC.
1. Prologue

**Disclaimer:** I do not own Yu Yu Hakusho.

**Author comments:** This prologue serves as an introduction to my OC and her relationship to the characters of YYH. Enjoy :)

* * *

**Prologue**

_[20 years ago]_

"What did you bring me?" Genkai asked.

The teenage Koenma gently adjusted the blanket-wrapped bundle in his arms to reveal a peacefully sleeping baby. "She was found my one of my men in the demon world," he explained. "All of her family members are dead. We're not sure where she came from and her spirit energy is different from ours. She's definitely a human though."

"And what do you want me to do with her?" Genkai asked suspiciously.

"Adopt her." Then he added quickly, "Just for a while so we can keep an eye on her."

"With all due respect Koenma, I'm not running a nursery here. And I'm not exactly what you would call the motherly type."

"I know, but please consider it as a favor to me. She would definitely die if we left her in the demon world."

Genkai looked at the curled up baby sleeping contently with its thumb in its mouth completely oblivious to the fact that its fate was being decided at that moment. Koenma thought Genkai's face softened ever so slightly.

"How long do I have to keep her?"

"However long you see fit."

Genkai sighed. "Fine, leave her here. But don't blame me if she gets killed by a demon or grows up incapable of normal human relationships."

"Uh not at all." Koenma said weakly as he passed the bundle over to Genkai. "Just, try to keep her alive."

"Does she have a name?"

"Yea, it's May, the month she was found."

_[12 years later]_

"Genkai! I'm leaving now!" A little girl with blue-gray eyes and brown hair that barely reached her shoulders stood at the entrance of Genkai's temple. She wore a light blue Yukata which looked odd with the overstuffed backpack on her back. In one hand she tugged a suitcase and in the other she had what appeared to be a newspaper clipping.

"School starts tomorrow?" Genkai asked.

"Yup! I called the owner of the house and told her I'd be arriving this afternoon so I can move in before school starts."

Genkai sipped her tea. "Alright. Try not to get into too many fights. If you must, then do it discreetly."

"Yes Genkai," May replied cheerfully and hugged her adopted mother goodbye. Then she skipped, or tried to skip as best as she could with all her belongings, down the mountainside towards the nearest train station.

"Let's see… It says 42 Magnolia Boulevard. This should be it!" May said happily looking from the newspaper clipping in her hand to the number 42 on the front door. She was not too good with directions but after three hours of walking she managed to find the place and she was feeling quite proud. Nevertheless, as she looked at the perfectly kept one story suburban house with its neatly trimmed grass and perfectly even walkway, she can't help but feel a bit nervous. She must've been standing outside the door staring for some time because suddenly it opened.

"Did you need something?" A boy about her age with bright green eyes and red hair asked.

"Um yes, I'm looking for Shiori Minamino. I'm renting the empty room."

"I see. That's my mom. Come in." He stepped back allowing May to follow him into the house. The inside of the house was simple but neat, and as she made her way towards the kitchen, the smell of chicken soup filled her nostrils and dissipated any uneasy feelings she had previously. Still she felt there was something odd about the boy.

"Mom, the tenant is here," the boy said to a woman in the kitchen.

"Oh thank you for getting the door dear. I didn't hear the knock." May immediately recognized the voice of the woman she spoke to on the phone. In person she had a kind face that seemed to hold a permanent smile. Her brown hair was pulled back in a low ponytail and she appeared to be the one responsible for the chicken soup. May liked her instantly.

"Are you May Hayashi?" She asked kindly from over the kitchen counter. "I didn't expect you to be quite so young."

"Yes Mrs. Minamino. Please call me May. Don't worry, I know how to do most chores," she said confidently.

"That's not what I'm worried about. You shouldn't be out on your own at this age. It's dangerous. Also, working while you're in school will affect your studies."

"Don't worry about that. I can take care of myself but I really need a place to stay so I can go to public school."

Mrs. Minamino looked concerned for a moment. Finally she said, "Alright, let's get you settled in first. Shuichi, would you please show her the room?"

May followed Shuichi to a room near the back of the house. It was a comfortable size and had one closet and a window but May noticed something missing. "Where's the furniture?"

"You didn't bring any furniture?" Shuichi asked.

"Umm I thought all rooms had furniture." May said sheepishly recognizing her mistake.

Shuichi stared at her for a moment as if he wasn't sure if she was joking. Then he went to tell his mom something and came back a minute later. "Let's go," he told her.

"Where are we going?"

"To get you a mattress."

It was just past 5 p.m. as the two kids walked towards the marketplace located just around the corner. May's strange feeling about the boy grew even stronger as they walked. Even though it was weak, she was sure she sensed demon energy coming from him. After fighting demons with Genkai for the last seven years, May was pretty confident in her ability to differentiate demon from non-demon, and this boy was definitely the former. However, he didn't seem evil and his mom was perfectly human.

"Which one would you like?"

"Hunh?"

"Which mattress would you like?" Shuichi repeated, looking at a row of twin size mattresses laid out in front of them.

"The cheapest one," May replied automatically.

They paid the cashier who told them that they will have it delivered by tomorrow. "Tonight you can sleep in my room and I'll sleep with my mom," Shuichi told her.

"Okay thanks," May replied absentmindedly. Then, before she can stop herself she blurted out, "You're a demon aren't you?"

Shuichi froze in his tracks. "You know about demons?"

"Yup. I grew up with Genkai so I'm used to fighting demons. I used to hate them because my family were all killed by demons but now I know not all demons are bad." Then she added "But if you try to attack me I won't hesitate to take you out."

"Don't worry I won't attack you. It's true I'm a demon, but I just want to live a peaceful life as a human now… as Shuichi."

"Who are you? If you're not Shuichi I mean. Why are you in this human body? How come your mom is a human?"

He contemplated for a moment what he should say. "I'll tell you but please don't tell my mom or anyone else."

May promised and Kurama told her who he really was.

After he was done, May stared at him for a long time. "So you're basically a 1000 year old fox demon living in a 12 year old human's body." Then she giggled. "No wonder you talk weird."

"What do you mean?"

"You don't sound like a 12 year old. You sound more like a butler."

Kurama laughed. "I see. I'll take that as a compliment."

May and Kurama became friends from that day forward. May stayed at the Minamino residence for three years and went to the same middle school as Kurama. Before high school began, she took on a part time job working for Koenma. She earned enough money so when high school started, she was able to rent an apartment of her own. Even though Kurama went to Meiou High, the two of them kept in constant contact. Later, May followed Genkai to the Dark Tournament where she met Yusuke, Kuwabara, Hiei, and the rest of the gang. The last she heard from Kurama he had told her that he, Hiei, and Yusuke were going to the demon world.

_[1 year later]_

_[The sound of a ringtone playing] Fukkiru hazu no kokoro ni sotto yokogiru kaze wa yasashi-_

May was in the middle of her sophomore year psychology class but as soon as she saw the caller ID on her cell she snuck out of the lecture hall. "Hello? Kurama?"

"Yes it's me. Are you busy?" Kurama asked.

May could hardly keep the excitement out of her voice. "When did you get back? How was the demon world? What happened to everyone?" A few students passing by gave her odd looks but she pretended not to notice.

"I got back yesterday. Everything is fine now. The demon world is unified under a new ruler and there shouldn't be any trouble in the human world for the next two years at least," Kurama explained. "Listen May, there's something I have to tell you. Can you meet me later?" Kurama's voice sounded troubled.

"Yea, I'm done after 3. Where do you want to meet?"

"Let's meet at 3:30 in the Garden café then."

When May arrived at the café, she saw Kurama was already there. He was seated at one of the tall chairs near the back corner of the café where there were not many people. She took the seat across from him. "Kurama?" His expression reminded her of the image of a little boy who just found out that Santa Clause wasn't real.

"May, I need to tell you something."

She waited for him to go on.

Kurama looked out the window. "Remember on the first day we met, you told me your family was killed by demons?"

"Yes."

"The demon that killed your family was Youko Kurama."

May was sure her heart stopped beating for at least five seconds.

"I found out from Yomi during this trip to demon world," Kurama continued wearily. "After I found out, I asked Koenma whether it was true. I'm so sorry. I didn't want to keep it from you."

May felt as if someone was choking her. "You killed my… but… why?"

Kurama sighed. "Your ancestors lived in the demon world for a short period of time but they were very well known in the region where they lived. There were many rumors saying that they were humans who came from another world and had hidden treasures with incredible powers. When the bandits and I heard of those rumors, we attacked them."

May looked at the man sitting in front of her as if she was seeing him for the first time. Tears were streaming down her face but she ignored them. "I hate you," she said before running out of the café.

* * *

**Author comments:** I actually had a lot of fun writing this prologue especially just imagining what a twelve year old May and a twelve year old Kurama would be like. I think deep down I'm still twelve. :D This intro focused a lot on the relationship between May and Kurama. I love how complicated their relationship is and I sympathize with both of them, especially May who is probably my alter ego. Their history will be important for the future development of the story and I'll leave it at that. Next chapter uploaded!


	2. No Turning Back

**Author comments:** Chapter 1 rewritten. Enjoy :) and as always reviews are greatly appreciated.

* * *

Chapter 1: No Turning Back

May woke up half an hour before her alarm went off. This was unusual for her but she was too preoccupied to go back to sleep so she pulled on a pair of jeans and a white shirt and went to the kitchen to make breakfast. She was preoccupied for two reasons. The first was her microbiology exam. The second was a certain meeting scheduled to take place later in the evening at Genkai's place. It would be the first time May will have to see Kurama since that day she ran out of the café almost a year ago. Since then she hasn't told anyone about what happened or what Kurama told her, not even Genkai.

_A 35 year old gardener presents with small raised ulcerations extending from his left index finger to his forearm. On further questioning, the man admits to being pricked by a thorn while weeding his rose garden last month. What is the most likely diagnosis?_

May closed her eyes and tried to summon the name of the fungus that caused these symptoms. Instead she saw a long slender rose whip with its prickly thorns. She wondered just how sharp those thorns were…

"Ten minutes remaining," said the professor.

May hastily circled _B. Sporotrichosis_ and moved on to the next question.

In the afternoon, May went to her biochemistry lab. She was clearly distracted and kept making mistakes. By the time she finally got out, the sun was setting and she was running late. She was the last to arrive at Genkai's temple.

"How nice of you to finally grace us with your presence," Genkai said sarcastically.

May apologized and took a seat on the floor next to Botan. She noticed Koenma, Kuwabara, Keiko, Shizuru, Yukina, and- yes- Kurama were also there.

"Alright since you're all here, let me get down to business…"

After Genkai finished explaining the details of her will, everyone started to get up. Someone said something about going down to the beach which was greeted with a chorus of enthusiasm from the rest of the group.

"May, can you stay for a bit?" Genkai asked.

"Of course."

"We'll be down by the beach," Keiko said before she followed everyone out.

Genkai waited for the group to get far enough before turning to May. "What is going on between you and Kurama?"

"Err what do you mean?"

"Don't play dumb. I raised you. I can tell when something's wrong. The two of you used to be close but I haven't heard you utter his name even once this past year. And today when you entered the temple you didn't so much as glance in his direction."

May sighed. "He… did something unforgivable."

"Did he cheat on you?"

"WHAT? NO! It's nothing like that!"

Genkai smirked. "Calm down, I was only kidding." She sipped her tea. "It must be pretty serious then."

May glared darkly at Genkai but decided to tell her the truth.

After she finished, Genkai didn't say anything for a while. She calmly finished her tea. "I understand why you're mad, but you will forgive him eventually."

"No I won't!" May said louder than she meant to.

"Then why didn't you tell me about it when you found out?"

"Why? Because it wouldn't have changed anything."

"You didn't tell me because you were subconsciously protecting him. You didn't want my view of Kurama to change. He was once a merciless demon so of course he's done terrible things, but as long as we distance ourselves from that fact, it doesn't matter. But once we are personally affected by those things, the character of Youko Kurama becomes that much clearer to us."

May didn't say anything.

Genkai continued. "You were always a stubborn child so if you're hell-bent on staying mad at him, there's nobody in the world who can change your mind. I'm only telling you to forgive him for your own sake. It takes a lot of energy to hate someone. Everybody makes mistakes but what's important is the present and you know the present Kurama better than anyone. That's why you still tried to protect him."

"Genkai you're giving me too much credit. I didn't talk about it because it's an unpleasant topic. I won't forgive someone who murdered my family, no matter who it is."

As May slowly descended the mountain steps towards the beach, she thought that maybe the reason she didn't tell Genkai was because she knew exactly what Genkai would say.

"May! Over here!" Botan called out, laughing and waving her hands in the air. Botan, Keiko, Yukina, and Kuwabara were all standing in the water, drenched from head to toe. And next to them was... Yusuke?

"He got back a minute ago and surprised us all," Koenma explained.

May smiled, took off her sneakers and ran to join the group of laughing kids by the ocean. As night fell, the kids reluctantly said their goodbyes and went their separate ways. Koenma received a call from spirit world so he and Botan were the first to leave. Eventually May found herself alone with Kurama. They got off at the same train stop. The two of them walked in silence as they passed by busy restaurants and night clubs populated by carefree teenagers enjoying their Friday night off. Kurama broke the silence first.

"I know you probably still hate me," he said softly.

"That's right."

"I won't ask you to forgive me but-"

"Good because I won't."

"But if there is anything I can-"

"There isn't," May said flatly, turning away.

A look of surprise flitted briefly over Kurama's face but it was soon replaced by an amused expression. "I see then that there's nothing I can do. It's good to know your stubbornness and impatience haven't changed in the past year."

"And your condescending attitude hasn't changed either," May said, feeling her temper rising.

BEEEEEP. BEEEEEP. BEEEEEP.

A sudden beeping noise came from the spirit watch on May's wrist. It flashed red in sync with the beeping. "It's Koenma," May said, wondering what on earth he could be calling her about at this hour. They ran over to a deserted alleyway and May pressed a button the watch. A miniature 3D projection of toddler Koenma appeared before them.

"Hi again," said the Koenma projection. Then he noticed Kurama. "You two are still together? I hope I didn't interrupt anything."

"You didn't. So why did you call me?"

"As a matter of fact, I do have something important to discuss with you. A couple of demons appeared to have escaped to the human world."

"And…?" May asked.

Koenma sighed, looking troubled. "I apologize for not telling you about this earlier," he continued, weighing his words carefully. "But we weren't sure about it until just recently… the existence of another human world that is. We think it's the world you came from May."

"Can you start from the beginning?" Kurama interrupted.

"Yes." The Koenma projection turned to May. "As you know shortly after you were born, a member of the spirit defense squad found you in the demon world."

May nodded.

"That was no accident. The reason we were looking for you was because of a rumor that started in the demon world."

"The rumor that my family came from another world," May filled in.

"That's correct. I'm glad Kurama told you that much. Anyway, King Yama wanted to see if there was any basis to that rumor so he sent someone to look for your family. Unfortunately, you were the only one we found alive and we were never able to confirm the rumor."

"So what did you guys do?"

"Even though we couldn't ask you about it, we still had reason to believe that you really did come from somewhere unknown to us. Your spirit energy, although human, is unlike any that we've ever seen. Even Genkai commented about it. That's why you couldn't be the successor of the spirit wave orb and Genkai had to find another disciple. Anyway, after we placed you under Genkai's care, we kept a close watch in the region where you were found. Over the years, we've noticed spatial disturbances at infrequent intervals which we think may be the portal that connects the demon world to the other human world."

"You said a couple of demons were able to cross over?" Kurama asked.

"Right. We're not sure how, but we know at least two demons have managed to disappear through a spatial distortion either on purpose or by accident. Either way, we have no idea what they're doing over there."

"So you want me to go and find out?" May asked.

Koenma thought for a moment. "It's more of an invitation. The decision is up to you because once you cross enter that world, we don't know how to bring you back. To be honest, no one else wanted to go and I can't force anyone because this doesn't directly affect the balance of our three worlds."

"I'll do it. I want to see what that world is like."

"That's what I thought you'd say."

"Then I will go too," said Kurama.

May stared at Kurama as if he had just announced that he was going to be married to an ogre. "This doesn't concern—"

"If her goal is to eliminate the demon, she'll have trouble depending on how strong the demons are," Kurama pressed on. "I would guess only class A or higher level demons would have the capability and intelligence to intentionally cross over. If she goes alone, it will be extremely dangerous, especially since we know almost nothing about that world."

"I can handle it," May said defiantly.

Koenma frowned and rubbed his chin. "It's not that I don't think you can handle it, but I would feel a lot better if someone went with you. We don't know what'll happen over there so having two heads is better than one, especially if one of those heads belongs to Kurama."

May scowled but didn't protest further.

"How long do we have before the next distortion?" Kurama asked.

The Koenma projection made a peace sign. "Two days."

After Koenma finished giving them the details of their departure and the projection faded, May turned to Kurama. "You know this doesn't change anything right?"

"I know nothing can make up for what I've done, but let me do this at least." Kurama's voice was so sad and gentle that May was caught off guard. He held out his hand. "Since we'll be doing this mission together, let's call a temporary truce."

"Okay…" May said, shaking Kurama's extended hand.

The next day May and Kurama were both kept busy making last minute arrangements and coming up with convincing stories to tell their family and friends about why they will be gone for the next indeterminate number of days. May kept her roommate from asking too many questions by telling her that she was dropping out of college to take on a top secret government job. Kurama on the other hand came up with a rather reasonable excuse and told his mom he wanted to travel the world with his friend before he settled down and inherited his stepdad's company. When his mom asked who the friend was and he told her it was May, she just smiled knowingly and told him to have a good time.

On the afternoon of their departure day, the May and Kurama met Koenma and Botan in the demon world near the edge of a place called the Jungle of Lost Souls. They both dressed lightly and carried only one backpack each. They watched as Botan fiddled with a strange device in her hand.

"All right, let's get this thing working," Botan said as she set the disc-shaped instrument on the ground and clicked a little red button in the center. The disc lit up and coordinates appeared across its surface.

"That is a spatial distortion sensor," Koenma explained. "If the distortion is close enough, people with high spiritual awareness should be able to sense it without problem. However this device is extremely sensitive and covers a wide area. When it detects a distortion, it will show up on the coordinates. We have to run to it before it disappears."

"How long does a distortion usually last?" Kurama asked.

"Anywhere from 1 minute to 10 minutes is what we estimated."

"What do we do when we find it?" May asked.

"You touch it," Koenma replied simply. "You will know exactly where it is and the moment you make contact with it, it will suck you in like a vacuum. That's about all I know of what will happen. After that, your guess is as good as mine."

"I see," May said nervously. It was just starting to dawn on her that she will soon be alone (well almost alone) in a strange world with no way of knowing when she can come back.

"Now, we just wait for the signal."

Three hours later, May, Koenma and Botan have taken up seats on a nearby rock under the shade of a large tree. Kurama was surveying the surrounding vegetation and seemed to have pocketed a few seeds from a couple rather intimidating looking demon world flowers. May tried not to think about what he might need them for. A few demons passed by as they waited. None of them paid much attention to the party of four except for an occasional curious glance. May watched as a little bear demon skipped happily by humming a tune that sounded a lot like "The itsy bitsy spider".

_Maybe_ _the demon world really has changed,_ May thought.

Then, she felt it. The sensor picked it up three seconds later and they were off. The distortion was only about a quarter of a mile deeper into the jungle and about thirty feet above the ground. She and Kurama led the way pushing aside thick demon world foliage as they ran. Koenma and Botan followed close behind.

"There's a demon close to it," said Kurama.

"You're right," May replied. "What should we do?"

"I'll see if I can knock it aside. If not we'll have to kill it," Kurama answered.

"You guys need to hurry, it's starting to close!" Botan shouted from behind them.

The distortion was situated above a large tree with gigantic leaves. The leaves conveniently blocked their view of both the distortion and the unsuspecting demon. Kurama jumped up the tree first, pulling out his rose whip on the way. May followed. She recognized the demon first before she noticed the distortion.

"Hiei! Get away from there!" Kurama shouted.

"Kurama!? What the hell are—"

It was too late. A gust of wind picked up and the tip of Hiei's black cloak grazed the shrinking space. The fire apparition vanished with a look of shock on his face. Kurama wasted no time jumping in and he too disappeared. By the time May reached the distortion it was only about the size of her fist. It reminded her of a mirage caused by hot air. She touched it and immediately felt as if she was pulled into a warm body of water. Everything faded to white. Somewhere in the distance, she thought she heard Botan and Koenma's voices shouting something, but she couldn't make out the words. Then just as she was starting to get used to the sensation, she felt pain. The pain was so excruciating she thought her skin was being ripped from her flesh. She screamed but no sound came out. Then, there was just darkness.

* * *

**Author comments: **What amazing things will they find in the other world? Stay tuned to find out. This chapter was a lot more difficult to write than I anticipated. The scenes played out well in my head but when I had to write it out, I had trouble deciding what things to focus on and what things to leave out. :/ Please review and let me know if any areas could be presented better, needed more clarification, etc.

The parts I enjoyed writing the most from this chapter were when Genkai indirectly teased May about her relationship with Kurama and when Kurama's mom "smiled knowingly" when he told her he was going to travel the world with May. It reminded me of one of those situations in life when everyone around you assume there's something going on between you and that other person when the reality of it is so far from the truth.

I'm not sure when the next chapter will be up since I'm in the middle of exams, but it will be up eventually so stay tuned. And I know the description says you don't need to know Hunter x Hunter to follow the story, you will appreciate it a lot more if you do. So if you haven't seen it and you like YYH, I recommend it to you with no reserve. It's made by the same creator.


End file.
